I hope he will not return because ummh I'm telling you my own opinion I feel the Rood doesn't belong in the demon world, so what if he was resurrected and proven as the demon king? so what? He have a rival remember it? and I'm sure Rood will just let Ruby to become the next King!! So what if he had the memories of the past Demon King [Raven]?, he is still Rood because he still remember his past life as a human, and Rood is scared to be alone again remember when Kiel and Rood finally met in the previous chapter? He is so scared to be alone again like the feeling that he felt when he was still a child. As long Rood has someone to return with, he can stay in the Human world because it is his home! To tell you the truth I think Rood don't have any home to return in the Demon world. And Rood already understand the whole situation he already graduated in his in denial stage!! He just want to know the explanation from his brother side. And he is intelligent enought to distinguished his difference from the others